Two-stage carburetor



5 Sheets-Sheet. 1

o. HENNING TWO-STAGE CARBURETOR April v29, 1958 Filed Aug. 1, 1955 INVENTOR. OTTO HENNING BY ATTORNEY April 29, 1958 o. HENNING TWO-STAGE CARBURETOR 5 Sheefcs-Sheet 3 Filed Aug. 1, 1955 FIG.3.

INVENTORQ OTTO HENNING ATTORNEY April 29, 1958 o. HENNING 2,832,576 TWO-STAGE CARBURETOR Filed Aug. 1, 1955 5 Sheets-Sheet 5 INVENTORQ' OTTO HENNING ATTORNEY nited States TWO-STAGE CARBURETOR Application August 1, 1955, Serial No. 525,522

Claims. (Ci. 261-23) This invention relates to fuel systems for internal combustion engines, and more particularly to multi-stage carburetor systems in which a plurality of carburetors or a plurality of mixture conduits in a multi-barrel carburetor are connected to a single intake manifold. Sinc multi-cylinder engines usually have dual manifolds, this system, when applied to each manifold, requires at least four individual carburetors or what is commonly referred to as a four-barrel carburetor.

The advantages of multi-barrel, multi-stage carburetors are well understood in the art, and are generally stated in many patents such as Kishline 2,193,533; Braun 2,434,192; Ericson, et al., 2,269,930, and others. A reference to these particular patents will fully acquaint those skilled in the art with sufiicient background to understood the present invention.

In some of these prior devices, the primary and secondary throttles are manually controlled in a sequential manner. In others, the secondary throttles open automatically in response to engine requirements. One of the disadvantages of all of the prior art devices is that, regardless of how the secondary throttles are controlled, their initial opening movement causes leaning out of the total mixture being supplied because there is always some lag in a plain tube type of carburetor before the fuel nozzles in the secondary carburetors begin to operate. This lag is readily detectable in many instances during rapid accoloration, and is indicated by a dip in the torque curve which is readily detectable by dynamometer tests.

The present invention solves this problem by modifications of the secondary carburetor, causing instantaneous fuel delivery on throttle opening.

In one modification an eccentrically pivoted air flow responsive valve is located in the secondary mixture barreis anterior of the fuel nozzles, rather than posterior thereofas in prior constructions such as Braun. The valve is providedwith a certain degree of mechanical unbalance resisting the opening force of the air pressures imposed on opposite valve surfaces when the secondary throttles are opened.

When there is sufficient air pressure differential on the valve to overcome the degree of mechanical unbalance, the suction posterior of the valve will usually be more than enough to cause rapid fuel delivery from the main fuel nozzle. Consequently, it is desirable to have a fuel valve for the main fuel nozzles which substantially shuts olf the fuel flow when the air valve is closed, but which will open proportionately as the air valve opens.

Such a means will cause the secondary barrels to function like an air valve carburetor, at least during initial operation. If desired, the degree of mechanical unbalance can be, and usually is, designed to decrease the valve closing force with valve opening, so that it be comes practically negligible when the valve reaches full open. The secondaries then function like a plain tube type of carburetor.

The results accomplished by this varied operation will eliminate the dip in the fuel ratio curve usually characatent teristic of multi-stage plain tube type carburetors. Before the secondary throttles open, engine suction acts directly on the fuel nozzle, and is therefore elfective during initial valve opening, so that there is no lag in fuel delivery from the secondary main nozzles. Simultaneous- 1y, airvelocity builds up in the secondary venturi to create the degree of suction necessary for continued fuel flow from the main nozzles as the suction producing effect of the air valve diminishes.

In another modification, the flow responsive valve is located anterior of the main throttle to initially close off all of the air flow except that through the primary venturi which encloses the outlet of the main fuel nozzle. The effect produced by this location of the valve is sim ilar to the action which can be obtained from a carburetor with a variable venturi.

Both modifications result in structures of reduced overall height while retaining conventional throttle construc tion, since it is unnecessary to provide additional room for a secondary controlling valve above or below the secondary throttle, as is required by Braun.

The accompanying drawings illustrate constructions which will operate to smooth out the transition point between the primary and secondary carburetors.

Other objects and advantages of the invention will be come apparent from the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a top plan view of a carburetor constructed in accordance with one modification of the instant invention.

Fig. 2 is a side elevation of the carburetor illustrated in Fig. 1, with parts broken away.

Pig. 3 is a vertical transverse sectional view of the carburetor of Fig. 1 taken on a plane through one primary and one secondary mixture conduit.

Fig. 4 is a side elevation of the carburetor in Fig. 1 illustrating the opposite side from Fig. 2, parts being broken away and sectioned.

Fig. 5 is a top plan view of the same type of carburetor illustrating a second embodiment of the invention.

Fig. 6 is a side elevation of the carburetor shown in Fig. 5, with parts broken away to illustrate the invention.

Fig. 7 is a fragmentary side elevational view of the opposite side of the carburetor from Fig. 6.

While more than one embodiment of the invention is shown in the accompanying drawings and herein described in detail, it is to be understood that his disclosure is given for the purpose of illustrating the invention, and is not intended in a limiting sense as to the precise constructions disclosed.

Throughout the drawings, similar reference characters represent similar parts, although, where such parts are modified in the structure, they may be indicated by differ ent reference characters.

The carburetor shown in Fig. 1 has four mixture conduits or barrels which, in this case, are grouped together. These include two forward main conduits 15 and 16 and two rear secondary mixture conduits 1? audit Air enters the generally rectangular air inlet portion 19 in the air horn, which is divided by a transverse partition 2% extending between the primary and secondary conduits. A shaft 21 extending transversely of the primary conduits and journaled for rotation in the side walls of the air horn mounts an unbalanced choke valve 22, which controls the opening on the primary side of the partition 20 and the entrance of air to the forward or main mixture conduits l5 and 16.

In this particular carburetor, the mixture conduits 15, 16, 1'7 and lb extend from the air horn 1 downwardly through a nozzle and float bowl body portion 2 and throttle body 3, all as shown in Fig. 2. Within the throttle body 3 are a plurality of throttle valves for controlling the flow of mixture through the several mixture conduits. This is better shown in Figs. 2 and 3. A primary throttle shaft mounts a pair of throttles 23 and 24, which will move simultaneously on operation of the throttle shaft 25. Secondary throttle shaft 26 mounts a pair of throttles 27 and 28 (Figs. 2 and 3) which separately control the secondary mixture conduits 17 and 18, respectively.

Primary throttle shaft 215 (Fig. 2) carries a double crank arm 29 rigidly fixed thereto. A suitable aperture 30 is formed in one end of the double crank arm 29 for attachment of the usual linkage extending from accelerator pedal of the vehicle. Another lever 31, also rigidly secured to the main throttle shaft 25, carries an idle speed adjusting screw 32. Small, disc-like member 34, rigidly secured to the corresponding end of the secondary throttle shaft 26, has a radially extending lug 35. Between and 7 above throttle shafts 25 and 26 is a stub shaft 37 carrying a fast idle cam element 38 and a freely rotatable lever 39. Lever 39 is rotatably connected to fast idle cam 38 by a lug 41 engaging within a socket 42 orrone radial face of the fast idle cam 33. A torsion spring on stub shaft 37 has one leg engaging arm 49 on cam 38 and the other holding lug 41 on lever 39 within notch 42.

Also loosely mounted upon the stud shaft 37 is an eccentrically weighted stop device 43, which, because of its weight distribution, normally assumes the position in which its one extreme end 44 is in the path of travel of the lug 35 on shaft 26, so as to prevent opening of the secondary throttle valves. The interaction of the finger 44 with the lug 35 provides a stable latch device which cannot be forced out of the way merely by the application of turning force to the shaft 26.

As shown in Fig. 2, lever 39 is connected by a rod 46 to an arm 47 rigid with the choke shaft 21. Accordingly, when the choke valve is closed, lever 39 is rotated from the position shown in Fig. 2 in a counter-clockwise direction, and lug 41 will move the fast idle cam 38 into a position to engage with the idle screw 32 and limit closing movement of the main throttle valves 27 and 23.

When the choke valve is open, fast idle cam 38 is urged in a clockwise direction by engagement of the lug 41 with one arm of the torsion spring 40. The reaction of the torsion spring on the fast idle cam lug 49 will tend to withdraw the fast idle cam 38 from engagement with the idle screw 32, so that, once the throttles 27 and 28 are opened, cam 38 will pull out of the way and the throttles may return to dead idle position.

Main throttle control arm 29 has an arm 48 movable with the throttle shaft 25 and so arranged that when the throttles are moved fully open, the end of this arm will engage a finger 49 on the fast idle cam 38 so as to rotate the lever 39 clockwise and thereby partially open the choke valve for unloading any excess fuel which may be in the intake manifold. When the choke valve opens under the influence of air flow and its thermostatic control mounted in housing 50, lever 39 rotates clockwise and lug 50, carried thereby, engages the eccentric weighted lever 43 so as to unlatch the secondary throttles 27 and 28. This structure is described in a co-pending application of Carlson and Moseley, Serial No. 263,291, filed December 26, 1951, for Throttle Control for Compound Carburetors, now Patent No. 2,715,522, issued Aug. 16, 1955.

The opposite side of the throttle body 3, as shown in Fig. 4, illustrates one way of interconnecting the primary and secondary throttle shafts for sequentially operating the secondary throttle shaft during opening movement of the primary throttle shaft. A resilient lost motion mechanism permits full rotational movement of the primary throttle shaft when the secondary throttle shaft is latched.

Loosely mounted on this end of the main throttle shaft 25 are a pair of levers and 56. A small, disc-like member 57 is rigidly secured to the end of the throttle shaft 25, and has an arm 58 interconnected by a coil tension spring 59 to the extremity of the lever 55. This spring normally maintains an outwardly turned finger 61 on the lever 55 in engagement with a radial finger 62 also formed integrally with the member 57. Lever 55 also has an inwardly turned peripheral finger 63 which lies in the same vertical plane as shoulder 64 on lever 56. Lever 56 has a struck-out lug 65 on its outer face for engagement with the abutment 66 on lever 55. Lever 56 is interconnected with lever 70 by a link 69. Secondary throttle shaft 26 is securely clamped to lever 70 by the bolt 71 extending through the legs of the bifurcated end of the lever 70. Tension spring 73 urges the secondary throttle shaft in a counter-clockwise direction for closing the secondary throttles 23 and 24.

Rotation of the primary throttle shaft 25 counterclockwise in order to open the primary throttles will not affect the position of the secondary throttles on the secondary throttle shaft 26 until the lug 63 on the arm 55 engages the shoulder 64. If the secondary throttle shaft is unlatched, further rotation of the primary throttle shaft to the full open position of the primary throttles will operate the levers 56 and 70 to fully open the secondary throttles. On closing of the primary throttles, abutment 66 engages lug 65 positively closing the secondary throttles.

if the secondary throttles happen to be latched during opening movement of the primary throttles, which can happen if the choke valve is not fully open, then the further movement of the primary shaft in a counterclockwise direction subsequent to the engagement of the finger 63 with the abutment 64 merely stretches spring 59. This construction and its operation are set forth more in detail in the above-mentioned co-pending application of Carlson and Moseley.

Formed on opposite sides of the mixture conduits are constant level fuel chambers 75 and '76 within which are pairs of floats 79 and 80, only two of which are shown in Fig. 4. Each pair of floats is interconnected by a yoke such as 81, one of which is shown in Fig. 4, and these are pivotally supported on suitable pins such as from suitable brackets suspended from the float bowl cover 86 by bifurcated elements such as 84. Needle valves such as 87 controlling the fuel passage 90 are engaged by the bifurcated elements 84 on movement of the pairs of floats 79 and 80 so as to maintain fuel at a substantially constant level in the fuel bowls 75 and 76, all in a well known manner.

Each pair of fuel chambers 75 and 76 is interconnected by cross-passages 91 and 92, within which are pairs of main fuel metering passages 93 and 94, one of which is shown in each of passages 91 and 92. Main fuel passages such as 95 and 96 connect with pairs of main fuel nozzles 97 and 98 within the primary venturi 99, 100

' located in the primary and secondary mixture conduits 15 and 17, respectively, as shown in Fig. 3. The main mixture passages 95 on the primary side of the carburetor have wells within which are restriction tubes 102 connecting by way of passages 103 with the usual idle ports 104 and 105 located on opposite sides of the throttle valves 24.

Primary metering orifice elements 93 are controlled by suitable metering pins 106, only one of which is shown, which are actuated in accordance with manifold vacuum and throttle position by means of a suction piston and spring element 107 and 108 working in a cylinder 109 connected to the primary mixture conduits posterior of the throttle valves therein by means of a suction passage 110. A stem 111 connected with piston 107 carries a cross-bar 112 on which are supported the pair of metering rods 106. Adjacent the cross-bar 112 is a countershaft 113 with a finger114 engaging beneath the crossbar 112. Countershaft 113 is operated, in turn, from the primary throttle lever 27 by means of a suitable linkage 116, part of which is shown in Fig. 2.

On the countershaft 113 and extending in the opposite direction from the finger 114 is a short lever 117 eonnected by means of a link 118 with an accelerating pump 119 within the well 120. Fuel from the fuel bowlenters the well 120 through passage 121 and leaves by way of passage 122 which interconnects by way of suitable valves and passages with nozzles 123, only one of which is shown, but both of which are located in separate primary mixture conduits 15 and 16.

So far, the description has been confined to the features shown and described in the aforementioned cpending application of Carlson and Moseley.

The present invention contemplates a modification of the multi-stage carburetor, which is more specifically shown in Fig. 3 and Fig. 4.

As shown in Fig. 3, the main fuel supply passages 96 leading to the fuel nozzles 98 in the secondary barrels 17 and 18 have valves provided with weighted bodies 125 and metering stems 126 projecting into and through a valve seat 127; An actuating stem128 for each valve projects through a guide 129 screwed into the upper end of a well 1311 in which the valve 125 is adapted to move. The upper ends of the stems 128 are joined by a transverse bar 131 which overlies a pair of fingers 132 rigid with a shaft 133 carrying the suction and velocity operated valve 134. The stem 128 may be shaped to control the air bleed 129. Shaft 133 is journaled in bearings in opposite sides of the air horn body 1, and has a projecting endto which is rigidly fixed an eccentric weight 136 .mounted on the shaft 133 so as to urge the valve 134 towards closed position. A lever 137 formed integrally with the counterweight 136 is connected by means of a link 138 to a rod 139 on piston 140. A dashpot cylinder 141 containing the piston 140 has an inlet check 142 controlilng the bowl inlet passage 143. Piston rod 139 is slidably mounted in the bearing 144 in the float bowl cover- 86 which is formed as an integral part of the air horn 1. Piston 140 has metered orifice 140a and overflow passage 145 leads from the port of cylinder 141 to the fuel bowl.

As can be seen, the parts are so interconnected that when the secondary barrels 17 and 18 are not in operation and throttles 27 and 28 are closed, velocity valve or throttle 134 will be held in closed position by the counterweight 136. A slight clearance will then exist between the finger 132 and the bar 131, so that valve 125 will remain seated by its own weight on seat 127, thereby preventing any spillage or leakage of liquid fuel from the main secondary fuel nozzles 98.

During operation of the engine with the throttles 27 and 28 partially open or full open, unless sufficient suction exists in the secondary mixture conduits, valve 134 will remain closed. When engine speed increases, suction will increase to a degree necessary to open valve 134.

Upon opening movement of valve 134, finger 132 ongages bar 131 to lift valves 125, so that fuel may flow through the main nozzles 98 to the secondary mixture conduits under control ofmetering rod 126. Weight 136 and dashpot 140, 141 will both resist opening movement of the valve 134 by engine suction, because the movement of the valve will force the piston 140 downwardly in the cylinder 141, compressing fuel beneath the piston 14% and retarding the progress of movement of the valve to a rate proportional to the leakage of fuel through the metered port 140a in the top of piston 140.

It will be apparent that, because of the mechanical connection controlling the operation of the valve 125 by the suction velocity valve 134, a difference in pressure must necessarily exist above and below the valve 134 to cause its operation in the opening direction. This difference in pressure can be predetermined by the degree of mechanical unbalance of the weight 136. It will be equally apparent that the rate of opening of the valve 134 due to this difference in pressure on its opposite sides can be likewise controlled by the dashpot action of the piston 140 in the cylinder 141, so that both the force ii necessary for initial opening and the difference in pressure necessary to produce a certain rate of opening will be required. Both differences in pressure, however, are subject to be determinedby proper calibration and testing of the individual carburetor.

During operation, when the secondary throttle valves 27 and 28 open, a certain amount of suction will exist beneath the valve 134, and this suction will be applied to main secondary fuel nozzles 98, but, since the valves are closed, no fuel will be discharged until there is some movement of the suction velocity valve 134. Upon opening movement of valves 125, however, fuel issues immediately from nozzles 98. The amount of flow will initially depend upon the degree of suction necessary to move the valve 134, rather than upon the velocity of air passing the main secondary fuel nozzles 98 through the venturis 11113. As the valve 134 moves toward its open position, its throttling action on the flow from the main nozzles decreases, and at some point during opening of the valve 134 may cease altogether.

At least initial operation of the secondary mixture conduits 'will resemble that of an anterior throttle type carburetor, but during final opening movement of the valve 134 the operation changes to resemble that of a plain tube type of carburetor.

Figs. 5' to 7 show another form of the invention applied to the same basic carburetor above described. The detailed description will therefore be limited to the modifications necessary in this basic structure. Like reference characters indicate parts corresponding to those already described.

Primary mixture conduits 15 and 16 have a common air entrance in the air horn 19 divided. by a partition 29 from the common air entrance to the secondary mixture conduits 1'7 and 13. The air horn entrance to the primary mixture conduits is controlled by a choke valve 22 mounted on rotatableshaft 21 and operated by the choke mechanism in the housing 5t all as above described.

The common air entrance to the secondary mixture conduits 17 and 18 mounts a pair of air valves and 151 which, when closed, confine the air flow to the inner venturi tubes 1% and 101i in the secondary mixture conduits 17 and 18, respectively. The inner free edge of the valve 150 has semicircular notches 152 and 153 which register with like notches 154 and 155 in valve 151 so astto accommodate or clear the inner venturi tubes While yieldingly closing the remainder of the secondary mixture conduits 17 and 18 to the passage of air when the valves are in the positions shown, except as above mentioned. 4

Each of the valves is mounted on a rotatable shaft such as 157 and 15% journaled in the walls of the air horn 1 Shaft 151% carries at one end a fixed arm 1519, the upper end of which has a pivoted connection with link 61}. Shaft 15? carries a compound lever fixed thereto, has a plurality of arms 161, 162, and 163. Link as a pivotal connection at its opposite end with he depending arm 161. With this construction, valves and 151 will move together or, when. one is locked against movement, both will be held closed. Also, since I; the valves are eccentrically mounted with respect to their shafts 157' and both will be responsive to suction when unlocked. The effect of suction in the secondary mixture conduits 1"! nd 13 is resisted by mechanical unbalance tending to hold the valves closed against the action of a diiference in pressure tending to open them. Arm 162 has a weight 154 for this purpose. Thus, as in the first form, the air valves constantly control the admission of air to the zone of the secondary mixture conduits into which inner venturi tubes 1% and 1% discharge fuel from the secondary main nozzles.

VALVE LOCK The lock for holding the valve against suction is operated by the automatic choke. Thus, in Fig. 6 choke arm 47 carries an arcuate latch member 166 which engages With a finger on arm 163 when the choke valve is closed. Release of this latch occurs when choke valve 22- reaches full open position, which, in turn, frees the two valves 150 and 151 to respond to differences in pres sure on their opposite sides.

It Will be noted that, because of this locking function performed by the choke valve, as above described, it is unnecessary in this modification of the carburetor to use a latch member such as 43 in Fig. 2 for holding the secondary throttles closed during operation of the choke valve. Furthermore, because of the omission of this particular latch mechanism, the linkage for sequentially operating the throttle shaft shown in Fig. 4 may be considerably simplified. A resilient interconnection between the primary throttle shaft 25 and the linkage for operating the secondary throttle shaft 26 may be omitted and, as will be noted in the description of Fig. 7 to follow, there is a total absence of a mechanism corresponding to arms 55 and 58 and their connecting spring 59.

In Fig. 7, primary throttle shaft 25 carries fixed thereto a disc-like member 170 having oppositely extending arms 171 and 1'72. An inwardly offsetlug 173 on arm 172 lies in the plane of lever 174, which is rotatably journaled on the throttle shaft 25. An outwardly extending lug 175 on the lever 174 is positioned to be engaged by the arm 171 when primary throttles 24 and 25 are in the closed position. Secondary throttle shaft 26 has fixed thereto an arm 17 7, and link 1176 has a pivotal connection with both arms 174 and 177. A spring 73 connects with arm 177 and the carburetor body to retain or urge the valve 27 in a closing direction.

With this mechanism, opening movement of the primary throttles 25 and 26 rotates lug 173 until it engages the edge of arm 174. At this point, throttles 23 and 24 will be open approximately 60 degrees. Further rotation of the primary throttle shaft in the throttle opening direction is transmitted to the secondary throttles 27 and 28 through the link 176 and arm 177 in such a manner that the throttles 27 and 28 reach their full-open position simultaneously with throttles 23 and 24-.

Rotation of the primary throttle shaft 25 from the full open position of the primary throttles in the closing direction permits spring 7 3 to move secondary throttles 27 and 28 to their closed position. This will occur when the primary throttles are still open about 60 degrees. Operation of the primary throttles to the dead idle position engages arm 171 with lug 175 so as to tightly close the secondary throttles 27 and 28.

Operation Generally speaking, the modification described in Figs. to 7 operates like a variable venturi carburetor when the air valves are unlatched by opening of the choke valve 22, and when latched closed there will be no interference with the normal carburetor operation during starting or warmup.

During engine cold starting, choke valve 22 will be closed, and the carburetor will function normally on the mixture supplied entirely by the primary mixture conduits. Movement of the primary throttles to operate the unloader 48 may open the secondary throttles to some extent, but, although valves 150 and 151 remain latched, the cranking speed is slow, relatively speaking. and no fuel will be drawn from the secondary mixture conduits.

When the engine is operating during the warm-up, both primary and secondary throttles can be fully opened without having the mixture lean out, because air flow is concentrated in the inner venturi tubes 1% and 108 in the secondary mixture conduits. A mixture-enriching effect will occur in the secondary mixture conduits suitable for warm-up.

During operation with the choke fully open, valves 150 and 151 are unlatched, but a certain degree of suction is required to cause them to open, which is determined by the degree of mechanical unbalance. This can be so chosen that all of the suction is concentrated on the primary venturi tubes and 100 on initial secondary throttle operation. This brings the secondary fuel nozzles into operation immediately on secondary throttle opening, and delivers a mixture suitable to eliminate any dip in the fuel ratio curve during the transition.

As the flow through the secondaries increases with engine speed and throttle opening, valves and 151 respond accordingly, increasing the size of the venturi nozzles. Preferably, valves 150, 151 will reach [full open position before maximum engine power output is reached.

The modifications above described and explained operate on a generally similar principle. During initial opening of the secondary throttles, the air valves throttle the flow of air to the zones of the secondary mixture conduits into which the secondary main fuel nozzles discharge, the air valves in both cases being located anterior to these zones, and, in so doing, create a substantial drop in static pressure, causing immediate fuel flow from the nozzles in the secondary mixture conduits which will be richer than otherwise.

In the first modification, the metering rod and valve 125, 126 and 127 may be properly shaped to give the normal mixture ratio after initial opening of the air valve 134. This may be controlled by the shape of the metering rod 126 or by opening of an air bleed for the secondary nozzles such as 129 by the valve 125.

In the second modification, the same control is effected by opening of the air valves 150 and 151, allowing the air to pass around rather than through the primary venturis 100 and 100'. The additional air reduces the mixture ratio to normal at any desired point in the opening.

As explained above, the mechanical unbalance for these valves in the form of weights 136 and 164 decreases in elfectiveness as the valve opens, which also tends to reduce the throttling effect and thereby lean out the fuel mixture.

A structure has been described which will fulfill all the objects of the present invention, but it is contemplated that still other modifications will occur to those skilled in the art which come within the scope of this invention as defined by the appended claims.

I claim:

1. In a multi-stage carburetor having primary and secondary mixture conduits, venturi tubes in said primary and secondary mixture conduits, primary and secondary fuel nozzles opening in said venturi tubes, and primary and secondary throttle valves in said mixture conduits posterior of said fuel nozzles, the combination of, a flow responslve member in said secondary mixture conduit anterior of said secondary fuel nozzle, a fuel valve controlllng the supply of fuel to said secondary fuel nozzle, and a connection between said member and said fuel valve.

2. In a multi-stage carburetor having primary and secondary mixture conduits, venturi tubes in said conduits, primary and secondary fuel nozzles opening in said venturi tubes, and primary and secondary throttle valves in said mixture conduits posterior of said fuel nozzles, the combination of, a flow responsive valve in said secondary mixture conduit anterior of said secondary fuel nozzle, a fuel metering device controlling said secondary fuel nozzle, and means interconnecting said flow responsive valve and said metering device for proportioning the fuel flow from said secondary nozzle in response to displacements of said flow responsive valve.

3. In a multi-stage carburetor having primary and secondary mixture conduits, venturi tubes in said primary and secondary mixture conduits, primary and secondary fuel nozzles opening in said venturi tubes and primary and secondary throttle valves in said mixture conduits posterior of said fuel nozzles, the combination of, an air flow responsive valve in said secondary mixture conduit anterior of said secondary fuel nozzle, fuel and air metering means for said secondary fuel nozzle, and a connection between said flow responsive valve and said air and fuel metering means controlling the delivery of fuel from said secondary fuel nozzle in response to movement of said flow responsive valve.

4. In a multi-stage carburetor having primary and secondary mixture conduits, venturi tubes in said conduits, primary and secondary fuel nozzles discharging into their respective venturi tubes, a choke valve and a primary throttle valve in said primary conduit, a secondary throttle valve means and an air flow responsive valve means in said secondary conduit on opposite sides of said secondary fuel nozzle and coacting to vary the fuel mixture, and means for locking one of said valve means in closed position, said locking means being unlocked responsive to opening movement of said choke valve, where by air flow through said secondary conduit is variably controlled by said valve means.

5. In a multi-stage carburetor having primary and secondary mixture conduits, venturi tubes in said conduits, primary and secondary fuel nozzles discharging into their respective venturi tubes, a choke valve and a primary throttle valve in said primary conduit, a secondary throttle valve means and an air flow responsive valve means in said secondary conduit on opposite sides of said secondary fuel nozzle and coacting to vary the fuel mixture, and means for locking one of said valve means in closed position, said locking means being unlocked responsive to opening movement of said choke valve, whereby air flow through said secondary conduit is variably controlled by said valve means, said air flow responsive valve means being anterior to said secondary fuel nozzle for throttling the flow of air entering said secondary conduit on initial opening of said secondary throttle valve means to enrich the fuel mixture.

6. In a multi-stage carburetor having primary and secondary mixture conduits, venturi tubes in said conduits, primary and secondary fuel nozzles discharging into their respective venturi tubes, a choke valve and a primary throttle valve in said primary conduit, a secondary throttle valve means and an air flow responsive valve means in said secondary conduit on opposite sides of said secondary fuel nozzle and coacting to vary the fuel mixture, and means for locking said secondary throttle valve means in closed position, said locking means being unlocked responsive to opening movement of said choke valve, whereby air flow through said secondary conduit is variably controlled by said valve means, said air flow responsive valve means being anterior to said secondary fuel nozzle for throttling the flow of air entering said secondary conduit on initial opening of said secondary throttle valve means to enrich the fuel mixture.

7. In a multi-stage carburetor having primary and secondary mixture conduits, venturi tubes in said conduits, primary and secondary fuel noules discharging into their respective venturi tubes, a choke valve and a primary throttle valve in said primary conduit, a secondary throttle valve means and an air flow responsive valve means in said secondary conduit on opposite sides of said secondary fuel nozzle and coacting to vary the fuel mixture, and means for locking said air flow responsive valve means in closed position, said locking means being unlocked responsive to opening movement of said choke valve, whereby air flow through said secondary conduit is variably controlled 'by said valve means, said air flow responsive valve means being anterior to said secondary fuel nozzle for throttling the flow of air entering said secondary conduit on initial opening of said secondary throttle valve means to enrich the fuel mixture.

8. In a multi-stage carburetor having primary and secondary mixture conduits, venturi tubes in said conduits, primary and secondary fuel nozzles discharging into their respective venturi tubes, a choke valve and a primary throttle valve in said primary conduit, a secondary throttle valve means and an air flow responsive valve means in said secondary conduit on opposite sides of said secondary fuel nozzle and coacting to vary the fuel mixture, and means for locking one of said valve means in closed position, said locking means being unlocked responsive to opening movement of said choke valve, whereby air flow through said secondary conduit is variably controlled by said valve means, said air flow responsive valve means being anterior to said secondary fuel nozzle for throttling the flow of air entering said secondary conduit on initial opening of said secondary throttle valve means to enrich the fuel mixture and comprising a pair of pivotally mounted coacting valves.

9. In a multi-stage carburetor having primary and secondary mixture conduits, venturi tubes in said conduits, primary and secondary fuel nozzles discharging into their respective venturi tubes, a choke valve and a primary throttle valve in said primary conduit, a secondary throttle valve means and an air flow responsive valve means in said secondary conduit on opposite sides of said secondary fuel nozzle and coacting to vary the fuel mixture, and means for locking one of said valve means in closed position, said locking means being unlocked responsive to opening movement of said choke valve, whereby air flow through said secondary conduit is variably controlled by said valve means, said air flow responsive valve means being anterior to said secondary fuel nozzle for throttling the flow of air entering said secondary conduit on initial opening of said secondary throttle valve means to enrich the fuel mixture and comprising a pair of pivotally mounted coacting valves interconnected by a linkage for common opening movement.

10. In a multi-stage carburetor having primary and secondary mixture conduits, venturi tubes in said conduits, primary and secondary fuel nozzles discharging into their respective venturi tubes, a choke valve and a primary throttle valve in said primary conduit, a secondary throttle valve means and an air flow responsive valve means in said secondary conduit on opposite sides of said secondary fuel nozzle and coacting to vary the fuel mixture, and means for locking one of said valve means in closed position, said locking means being unlocked responsive to opening movement of said choke valve, whereby air flow through said secondary conduit is variably controlled by said valve means, said air flow responsive valve means being anterior to said secondary fuel nozzle for throttling the flow of air entering said secondary conduit on initial opening of said secondary throttle valve means to enrich the fuel mixture and comprising a pair of pivotally mounted coacting valves interconnected by a linkage for common opening movement, and having recesses therein to receive their related venturi tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,571,611 Vincent Feb. 2, 1926 1,840,279 Sturrn Jan. 5, 1932 1,929,193 Teeter Oct. 3, 1933 2,420,925 Wirth May 30, 1947 

